Method and apparatus for surveying wells



RECORDING METER 2 Sheets-Sheet l AMPLIFIER R. G. PlETY Filed March 17,1941 April .13, 1943.

METHOD AND APPARATUS FOR SURVEYING WELLS FIG? .INVENTOR R.6. PIETY BY zI 4 Z Z ATTOR YW April 13, 1943. R, G I Y 2,316,361

METHOD AND APPARATUS FOR SURVEYING WELLS Filed March 17, 1941 2Sheets-Sheet 2 ECORDING MPLIFIER v METER 69 FIG. 4

'INVENTOR R.G. PIETY ATT Patented Apr. 13, 1943 METHOD AND APPARATUS FORSURVEYING WELLS Raymond G. Piety, Bartlesville, kla., assignor toPhillips Petroleum Company, a corporation of Delaware Application March17, 1941, Serial No. 383,818

16 Claims.

This invention relates to improvements in method and apparatus fordetermining the radioactivity in bore holes.

Radioactivity has been found to be associated with the various earthstrata in varying amounts. The radioactivity of the earths rocks is, forall practical purposes, constant. Of the sedimentary rocks, shales arethe most radioactive, the black or dark colored shales being far moreradioactive than any of the other rocks. Sandstones and limestones arethe least radioactive, the sandstones being generally less radioactivethan the limestone. Although the concentrations of radioactive materialsin the earth's formations are generally very small, the radio activityof the rocks is sufficient to furnish a means of correlating the variousstrata. It is known at present that the Geiger counter, an instrumentwell known to the physicist, may be used to detect the gamma rays fromradioactive materials associated with the earths strata and wellsurveying instruments employing the Geiger counter have been devised.Such an instrument is shown and described in the co-pending applicationof R. G. Piety and H. H. Kaveler, Serial No. 329,810, filed April 15,1940.

In logging a well for radioactivity with an instrument employing aGeiger counter, usual practice is to enclose the Geiger counter in asuitable housing which excludes well fluids but allows gamma rays topass through; Radiations from all directions strike and activate theGeiger counter although most of the radiations affecting the instrumentare from the nearby surrounding formation. It is difficult to determinewith this instrument the exact depth at which the instrument passes fromone geological strata to another exhibiting a different amount ofradioactivity. If a natural geological marker, or a marker of the typedisclosed in the above mentioned application of Kaveler and Piety, isused as a reference point from which measurements are made, it isessential that the marker be accurately located to insure accuracy ofthe measurements. The present invention provides apparatus foraccurately determining the position of such a marker.

An object of this invention is to provide apparatus of increasedresolving power for determining variations in radioactivity of the earthformations pierced by a Well bore.

Another object of this invention is to provide a method of and apparatusfor determining the direction of inclination of earth strata pierced bya well bore.

Still another object of this invention is to provide apparatus fordetermining the angular distribution of radioactive materials about awell bore,

Often a geologist is interested in the direction of inclination, in theangle of inclination or the dip, and in the direction of intersectionwith a horizontal plane, or the strike, of the various strata pierced bya well bore. Heretofore it has been possible to determine the dip andstrike of any particular subsurface stratum only by drilling three holesinto the stratum. The present invention provides a method and apparatusfor determining the strike and approximating the dip of a stratumpierced by a single bore hole. This method is based on the difierence inthe radioactivity of adjacent strata.

The angular distribution of radioactive ma-- terials in the formationssurrounding a bore hole may be variable due to either natural variationsin radioactivity or to a radioactive marker previously placed in theformation as disclosed in the aforesaid patent application of Kavelerand Piety. The angular distribution is determined in the presentinvention by novel apparatus which is directional. This apparatusenables an operator to determine the exact position of a radioactivemarker or formation of interest and to determine the azimuth of such amarker. The operator may thus obtain a reference direction in the wellbore for reference in locating other equipment.

The invention, its objects and advantages, will be more clearlyunderstood from the following detailed description and the accompanyingdrawings.

Figure 1 is a diagrammatic view of one embodiment of the presentinvention.

Figure 2 is a cross-section taken along the plane 2-2 of Figure 1.

Figure 3 is a diagrammatic view of a modification of the apparatus ofthe present invention.

Figure 4 is a diagrammatic view showing the apparatus of Figure 3 inoperating position in a bore hole.

With reference to Figures 1 and 2 of the drawings, a well surveyinginstrument, designated generally by the numeral 5, is shown in operatingposition in a bore hole 6. The instrument housing I of steel or othersuitable metal excludes the well fluid but allows passage of gamma raysinto its interior. The surveying instrument is suspended in the borehole by a cable 8 containing a pair of electrical conductors. The cableis supported at the surface of the earth ing instrument in the borehole.

by a reel 9 which serves to position the survey- Contact between theelectrical conductors in cable 8 and electrical equipment at the surfaceof the earth is established through slip ring and brush connections l9and l l on the reel. Inside the housing I of the surveying instrument isa cluster of three Geiger counters l2. Lead shields l3 and H arearranged to shield the counters from radiations coming from anydirection other than at right angles to the axis oi. the surveyinginstrument. The arrangement of the Geiger counters within the housingand lead shields will be apparent from Figure 2. Radiations from thesurrounding formation passing through the housing I may enter thechamber defined bythe lead shields l3 and i4 only by passing through theopening i5 between the shields.

Geiger counters are well known; it is suflicient for the purpose of thisinvention to state that they allow a pulse of current to flow throughthe counter circuit when activated by a gamma ray. The efficiency of theGeiger counter is low, on the order of 5 to per cent, therefore many ofthe gamma rays pass through the Geiger counter without activating it. Tomake the surveying instrument more sensitive, the Geiger counters i2 areconnected in parallel in the counter circuit and supplied with currentfrom a common source. It is possible to increase the sensitivity of thesurveying instruments nearly in direct proportion to the number ofcounters used in parallel.

Power is supplied to the Geiger counters from a source l5 of highvoltage, direct current. Current from the source ,i6 flowing through thecounter circuit and through any of the Geiger counters passes throughthe primary winding of the transformer i1.- Current generated in thesecondary of the transformer I1 is transmitted to the surface of theearth by electrical conductors l9 and i9 which pass through the cable 8.

This'current is picked up at the reel 9 by the slip ring and brushconnections i9 and ii, and transmitted by electrical conductors 20 and 2i, to the amplifier 22 and the recording meter 23. Thus the recordingmeter 23 records the pulses of current flowing through the countercircuit due to activation of the Geiger counters by gamma rays. Theapparatus, which receives gamma rays only from the formation directlyopposite the Geiger counters, gives improved accuracy in locatingmarkers and a sharp delineation of natural radioactive variations,

The modification of the invention shown in Figure 3 of the drawingsprovides means for the determination of the angular variations inradioactivity and of the directions of such variations. The surveyinginstrument in this instance is suspended in a bore hole 39 by a cable 3|attached to the housing 32 of the instrument. The cable is carried by areel 33 at the surface of the earth by which the surveying instrumentmay be extended or retracted along the bore hole. Within 7 the housing32, a prime mover 34 is mounted on -a gimbal so that it will remainplumb or level when the housing is tipped. The gimbal consists of a ring35 in which the prime mover, pivoted on pins 36, can turn on an axisthrough the ,dIameter of the ring while the ring 35 is pivoted on thepins 31 so that it is free to turn on an axis at righ't angles to, thatof the. prime mover. The prime mover 34 may be aclockworkmotor or anelectrical motor of the selsyn or asynchronous type. carried byandconnected to the shaft 38 recording meter I i.

of the prime mover is a lead shield 39 which is revolved slowly by theprime mover. within the hollow interior of the shield 39 is a Geigercounter 40. Radiations from radioactive substances in the formationssurrounding the bore hole may reach the Geiger counter by passingthrough the opening 4| in the shield. The Geiger counter is efiectivelyshielded from the action of gamma rays from portions of the formationother than that directly opposite the opening 4|. A bail 42, attached tothe exterior of the prime mover 34, extends up over the shield 39 andsupports the Geiger counter in its proper position within the rotatinghousing. Power is supplied to the Geiger counter from a source 43 ofhigh voltage direct current. The counter circuit comprises the currentsource 43, the primary winding of a transformer 44, and the Geigercounter 40. The insulated wires 45 and 46, by which the power from thesource 43 is transmitted to the Geiger counter, are flexible to permitfreedom of movement of the Geiger counter and the supporting bail 42.

Attached to the prime mover 34 and extending below it is the portion .50of the compass housing which serves to support the compass and shieldthe compass needle from electrical interference. The magnetic compassneedle 5! is pivoted on a bearing 52 which is mounted on thenonconducting lower portion 53 of the compass housing. An insulatedbearing 54 is mounted in the upper portion of the compass housingdirectly above the bearing 52. The shaft 55 extends through theinsulated bearing 54 and is driven by the 58 extending downwardlytherefrom. On one end of the compass needle, preferably the northseekingend, is a corresponding spark point 59. A metallic ring 60 on theinsulated portion 53 of the compass housing surrounds the compass needleat a fixed distance from its ends. The metallic ring is connected to onepole of the current source 43 by the conductor Bl The conductor 62 fromthe opposite pole of the current source is connected to the arm 51through the bearing 54. When the spark point 53 on the rotor is directlyabove the corresponding point 59 on the compass needle, a spark isformed between the points 58 and 59 and a spark is formed also betweenthe compass needle 5| and the metallic ring 69. Whenever this sparkingoccurs, a pulse of current from the source 43 flows through the primarywinding of the transformer 44. For the magnetic compass hereindescribed, an equivalent, the gyro compass may be substituted whereverdesirable, or because of difiiculty experienced in use of a magneticcompass under the particular conditions of the survey.

Pulses of current flowing through the primary winding of the transformer44, due to activation of the Geiger counter by gamma rays or to sparkingin the compass, generate corresponding pulses of current in thesecondary winding of the transformer. These are transmitted to thesurface of the earth by the electrical conductors 64 and 55 which passthrough the cable 3|. Slip ring and brush connections 36 and 61 pick upthe current at the cable reel 33 from which it is transmitted byconductors 63 and 39 to an amplifier l0 and The recording meter recordsthe pulses of current due to the Geiger counter and the compass. Thepulses of current due to the Geiger counter are a measure of thePositioned radioactive markers to orient equipment radioactivity of thatportion of the formation directly opposite the opening 4| in the leadshield 39. The pulses of current due to the compass, which are ofgreater intensity, occur only when the rotor 51 passes directly over thenorth-seeking end of the compass needle 50. The chart of the recordingmeter may be driven in any suitable manner, such as by clockwork, aselsyn motor, or an asynchronous motor, that will allow correlation ofthe data obtained in the bore hole. By interpolation on the chartbetween pulses recorded each time sparking occurs in the compass, it ispossible for the operator to determine the directions from whichradiations are received by the Geiger counter as determined by therevolving shield 39. This is especially useful in determining the dipand strike of subsurface strata.

For example, in Figure 4, the numerals 12 and 13 refer to stratainclined with respect to the axis of the bore hole and having associatedtherewith different amounts of radioactivity. During a part of therevolution of the lead shield 39 emanations from radioactive materialsin the stratum 73 enter the opening 4| and activate the Geiger counter40. During another part of the revolution emanations from theradioactive materials in the stratum 12 enter the opening 4|. Bycorrelation of the directional variations in radioactivity and itsangular distribution about the Geiger counter the geologist may readilydetermine the strike of the strata i2 and I3. A series of thesedeterminations at known positions along the bore hole may be utilized toapproximate the dip of strata when the bore hole is uniform and of knowndiameter. The same instrument may be used in an analogous manner todetermine the inclination of the bore hole 30 in localities where thedip of the subsurface strata l2 and 13 is known or in the same bore holeafter the dip of the strata has been determined. When used to determinethe inclination of the bore hole, the gimbals are rendered inoperativeso that the axis of the Geiger counter and shield coincides with theaxis of the housing 32. This instrument may also be used in conjunctionwith in a well bore, e. g., the direction from which a core is takenfrom the side of the bore hole may be determined. By depositing a smallamount of radioactive material at the time a side wall core is taken,the apparatus of Figure 3 may then be used to determine the position anddirection from which the core was taken from the side wall.

It is not anticipated that every formation will possess sharply definedboundaries and radioactive contrasts which will allow the orientation tobe determined without uncertainty. In general it is true that there areseveral beds which are conformable so that several determinations may beaveraged. The determination of the horizontal projection of thedirection of maximum dip is of considerable help in interpreting corestaken and may be used in many cases to determine the actual orientationof the core when it was in place. In the event that there is aconsiderable variation in the permeability of the formations penetratedit is possible to force varying amounts of radioactive fluid into theformation prior to use 01' the surveying instrument to greatly increasethe activity. of the porous formation.

It is to be understood that various changes in size, shape, and relativeposition of the parts comprising the apparatus of my invention may beresorted to without departing from the spirit of the invention.

I claim:

1. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing in the bore holea directional detector responsive to radioactive radiations, andobserving the direction and response of said detector with respect to areference point on a magnetic compass.

2. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing in the bore holea detector responsive to radioactive radiations striking the detectorfrom a given direction, varying the direction of response, and observingthe variations in the response of the detector with variations in thedirection.

3. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing a detectorresponsive to radioactive radiations in the bore hole, rotating thedetector at a substantially constant speed, and observing the variationsin the response of the detector during rotation.

4. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing a detectorresponsive to radioactive radiations in the bore hole, exposing thedetector to radiations from a limited section of the surrounding earthat a point along the axis of the bore hole, successively exposing thedetector to radiations from different sections of the earth surroundingthe well bore at said point, observing the directions of the diiferentsections and observing the variations in the response of the detectorupon being exposed to said sections.

5. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing in the bore holea directional detector responsive to radiations from radioactivematerials, changing the position of said detector to receive radiationsfrom difierent directions about the axis of the bore hole, and observingthe variations in the response of said detector with changes in itsposition.

6. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing in the bore holea detector responsive to radioactive radiations, shielding a portion ofthe detector from radiations entering the bore hole from the adjacentearth formations, determining the direction of the exposed portion ofthe detector, and observing the response of said detector.

7. The method of determining the distribution of radioactive materialsin the earth surrounding a bore hole comprising placing a detectorresponsive to radioactive radiations in the bore hole, shielding thedetector from radiations entering the bore hole from certain directions,varying said shielding to vary said directions, and observing variationsin the response of said detector with variations in said directions.

8. In the method of surveying a bore hole by observation of theradioactivity associated with the earth surrounding the bore hole, theimpre'iement which comprises placing a detector responsive to thedirection and frequency of radioactive radiations in the bore hole andobserving the response of said detector with variations in its directionand position in the bore hole.

9. The method of surveying a borehole comprising suspending in the borehole a detector responsive to radioactive radiations received by thedetector from a given direction, and determining bore hole comprising adetector responsive to ra-- dioactive radiations from a given direction,

means for suspending the detector in the bore hole, and means forindicating the direction from which the radioactive radiations arereceived by the detector.

11. Apparatus for determining the relative radioactivity of earthformations surrounding a bore hole comprising a detector responsive toradioactive radiations, means for supporting the deftector in the borehole, and means for limitin the portion of the earth to which thedetector is exposed. and means for indicating the direction of saidportion of the earth.

12. Apparatus for determining the relative radioactivity of earthformations surrounding a bore hole comprising a detector responsive toradioactive radiations, means for supporting the detector in the borehole, and a directional shield for limiting the portion of the eartharound the bore hole to which the detector is exposed, and means forindicating the direction of said portion of the earth.

13. Apparatus for determining the relative m:

dioactivity of earth formations surrounding a bore hole comprising adetector responsive to radioactive radiations, means for supporting thedetector in the bore hole, and a shield having an opening thereinrotatable about an axis substantially parallel to the axis ofv the borehole, said opening admitting radioactive radiations to the detector, andmeans for determining the position of the shield during rotation.

5. 14. Apparatus for determining the relative radioactivity of earthformations surrounding a bore hole comprising a detector responsive toradioactive radiations, means for supporting the detector in the borehole, and a directional shield associated with the detector, means forrotating 'the shield to vary its effective direction, and means fordetermining the efiective direction of the shield during rotation.

15. Apparatus for determining the relative radioactivity of earthformations surrounding a bore hole comprising a detector responsive toradioactive radiations, means for supporting the detector in the borehole, and a shield substantially impervious to radioactive radiationslimiting the receipt of radioactive radiations by the detector to thoseentering from an angular segment of the bore hole substantially normalto the axis of the detector, means for changing the direction of thesegment from which radiations are received relative to the detector, andmeans for indicating the direction of said segment relative to thedetector.

16. Apparatus for determining the relative radioactivity of earthformations surrounding a bore hole comprising a detector responsive toradioactive radiations, means for supporting the detector in the borehole, and a directional shield associated with the detector limiting thedirection relative to the axis of the bore hole from which theradioactive radiations may be received by the detector to a directionsubstantially normal to the axis of the bore hole and means fordetermining the direction of the receipt of the radiations relative to aplane normal to the axis of the bore hole.

RAYMOND G. PIEI'Y.

